There is a major health and environmental concern regarding emitted particles from vehicle exhaust pipes, in particularly from Diesel engines. Particles, having a size ranging from nanometers to micrometers (herein after referred to as “submicron particles”), impose risk to the health and to the environment. Since the submicron particles are small in size, it is easier for the submicron particles to penetrate the respiratory system. Furthermore, the stay time of smaller size particles in the air is much longer. For example, a particle of 0.1 micron will stay about 100 times longer in the air than a particle of 1 micron. Hence, submicron particles impose a two-fold risk: (a) longer exposure and (b) easier penetration to the lungs. This risk is described in numerous academic papers as well as in the US-EPA website. Emitted particles also harm vegetation and even the surface of buildings and monuments. The term “inhaleable particles” is used herein interchangeably with the term “submicron particles”.
Hence, increasing a particle's size at the expense of reducing the number of submicron particles will reduce the above mentioned risk impose by submicron particles to the health and environment. The term “filterable particles” as used herein refer to particles large enough such that inhaling organisms of living subjects in general, and those of human beings in particular, are capable of filtering the filterable particles, thereby preventing filterable particles from entering the lungs. Filterable particles also correspond to particles which can be captured by a mechanical filter.
The grouping of submicron particles brings to coagulation and to the formation of larger size particles and thereby decrease the number of submicron particles. There is therefore a need and it would be advantageous to have an apparatus that groups submicron particles into larger size particles, preferably filterable particles, and thereby decrease the number of submicron particles, for example, submicron particles departing from the exhaust system of an engine such as a Diesel engine.
A mathematical analysis concerning the grouping of submicron particles, is found in D. Katoshevski, “Characteristics of Spray Grouping/Non-Grouping Behavior”, Aerosol and Air Quality Research, Vol. 6 (1), pp. 54-66, 2006. The analysis shows that when the velocity of the matter carrying the submicron particles, such as air, has a form of a moving wave, particles that are carried by such a wave may form groups under specific range of parameters. Such a wave exists in various systems such as in the case of particles in the sea-water where the wave is moving, described in Winter, C. at al, “Grouping Dynamics of Suspended Matter in Tidal Channels”, J. Geophysical Research (JGR), Vol. 112: C08010, doi: 10.1029/2005JC003423, 2007.